I'm researching the story that the Christian Apostle Simon -- later Saint Peter -- was actually a Jewish plant who was instructed by the rabbis to change Christian observances and beliefs to make it much more distinguishable from rabbinic Judaism. Dr. Shnayer Leiman, of YU, mentions a 1705 un-censored version of Toldos Yeshu as a prime source for this. Does anyone know where I can find it?

There is a Sefer called "Otzer HaMedreshim" (I know it's rather "general" but that's what it's called!) that I once saw that brings down the story about Shimon HaKeifeh (also known by different names) who is the one that you are referring to (based on Dr. Leiman's article on this issue and the sources cited there -- The Baruch Tam being probably the main and best known source for this in halachic seforim (however there is at least one more as Dr. Leiman brings down.)

The article for those that are interested in this fascinating analysis of Tes Teves and the history behind it, together with the story the questioner is referring to can see it here.

That's excellent - thank you! On p176, where it appears to quote a section of this text, it cites the source as being ספר הלכות גדולות. Is that a typo? Why is it citing the Semag?
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Shimon bMDec 28 '12 at 1:18